Method of working steel, and products thereof



Patented Apr. 7, 1942 METHOD OF WORKING STEEL, AND PRODUCTS THEREOF Henry S. Schaufus, Baltimore, Md., assignor to Rustless Iron and Steel Corporation, a corporation of Delaware No Drawing. Application October 31, 1938,

" Serial No. 238,082

1 Claim.

My invention relates to stainless iron and steel products, particularly to those products used in the fabrication of various articles wherein coldupsetting, deep-drawing, or like sever forming operations are encountered.

Among the objects of my invention is the provision, in a simple, efficient and thoroughly reliable and practical manner, of stainless iron and steel bars, rods and wire, plate, sheet and strip, and like products which are particularly suited to comparatively severe cold-forming operations, such as, cold-heading, punching, stamping, trimming, deep-drawing and the like, with a minimum of checking, splitting or other damage to the metal and with a minimum of wear and breakage of forming dies, punching, trimming or other processing tools.

The invention accordingly consists in the combination of features, in the combination of steps and the relation to each of the same to on or more of the others as described herein, the scope of the application of which is indicated in the following claim.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that the stainless irons and steels find considerable favor in the railway car body, automotive, culinary equipment and like industries. The metal is especially suited to the production of various screws, studs, nuts, as well as small parts of trim where a corrosion-resistance is required or where there is desired a bright surface appealing to the eye. Such manufactures are produced from metal in form of plate, sheet and strip, as well as bars, rods, and wire. In this production certain rather severe coldforming operations are commonly employed. For example, in the production of screws, steels and nuts, metal in the form of rods and wire is subjected to cold-heading and other cold-upsetting operations. In the production of certain of these, especially the Phillips head screws, the cold-heading operation is particularly severe.

In many of the more severe cold-forming operations, the metal checks and splits in the forming dies. This frequently results in a jamming of the forming machine, high wear of processing tools, as well as giving a high loss in product. Both of these results aredistinctly undesirable.

As a further result of cold-forming operations, there is in stainless iron and steel a very distinct hardening of the metal. This phenomenon is observed in the ferritic and martensitic steels (those containing to 35% chromium, with carbon up to .30%, and the balance iron),'and

especially in the austenitic grades (those containing 10% to 35% chromium, 6% to 35% nickel, with carbon up to about .20%, and the balance iron). The work-hardening of the metal becomes most objectionable where especially severe cold-forming operations are performed. This results in a perceptible lowering of the life of the forming dies, as well as a high breakage loss.

Accordingly ne of the objects of my invention is the provision of a simple, emcient and practical method of achieving stainless steel products which are especially suited to cold-forming operations, giving good results in cold-heading, deep-drawing, and the like, with minimum loss of time and material and with maximum lif of the forming dies. In this connection, it is understood that my invention pertains to stainless steels of the character noted above, wherein there may be present one or more of the common ingredients, such as, aluminum, silicon, molybdenum, copper, tungsten, vanadium, titanium and columbium.

Referring now more particularly to the practice of my invention, I find that the cold-forming properties of stainless iron and steel products are greatly improved by giving the same a certain final critical cold reduction of between 3% and 15%, followed by a short annealing treatment and a quick cooling to room temperature. These products are in form of plate, sheet and strip, or bars, rods and wire. For the plate, sheet and strip, the critical cold reduction is had as a final cold-rolling operation, while for the bars, rods and wire the final cold reduction is a cold-drawing operation, In both groups of products the reduction in sectional areais had to about the same degree.

In the ferritic and martensitic grades of stainless steel, those containing chromium in the amount of about 10% to 35% with the balance iron and impurities, as well as common additions in amounts insufilcient to change the essential characteristics of the metal, it is my observation that a cold-reduction of 3% to 15% is required.- Apparently, best results are had where the cold reduction is about 10%.

In the austenitic grades, those containing chromium in the amount of about 10% to 35%, nickel in the amount of about 6% to 35%, and the balanc iron and common additions, the required reduction in sectional area is 3% to 12%. With this grade of stainless iron or steel, best results are had where the amount of cold reduction is about 5%.

As a second step in my treating operation, the products are annealed. I iind that a long annealing treatment is not required. It seems that a short anneal gives satisfactory results. Usually it is only necessary that the products be heated sumcientl long to permit the heat to pentrate the interior of the metal and a substantially uniform high temperature achieved throughout. While the temperature or the annealing treatment may well fall within a fairly wide range, in accordance with the amount of chromium and nickel present, I find best results are realized where a temperature of about 1800- 2200" F. is employed for the austenitic steels, and 1400-l800 F. for the ierritic and martensitic steels. Preferred temperatures are 2000' F. for the former type and 1550 I". for the latter types. It will be understood that this annealing treatment is had immediately after the final cold-reduction of the metal in the critical amounts noted above. For this purpose, known annealing ovens or other heating apparatus are employed. Bright annealing furnaces are particularly suitable for this work. also are had with the continuous furnaces on production work.

Following the annealing operation, the products, as withdrawn from the annealing furnace, are, cooled to room temperature. This may be considered as a third step in my treating operation. Ordinarily the products are of such size that the heat is dissipated sufllciently rapidly by a simple cooling in air. Where large sections are being treated, however, it will be understood that a quench in oil or water may be used. 01'- dinarily the annealed products are pickled to achieve a desired smooth surface, although this treatment may be omitted where a bright annealing operation is employed instead of the conventional annealing treatment.

Stainless iron and steel bars, rods, and wire, treated in accordance with my process, readily may be cold-headed, cold-upset in the production 01', for example, screws, nails and studs, or otherwise cold-worked, with a minimum of loss through tearing or splitting of the metal. Likewise, plate, sheet and strip so treated is readily deep-drawn without tearing in the drawing dies. Moreover, I find that the metal hardens less as a result of the cold-forming operations giving Good results less wear of the forming dies and a consequent increase in die life. As a further advantage, breakage or dies through the jamming oi the forming machine by the damaged products also is reduced to a minimum.

I attribute the improved cold-forming characteristics of stainless iron and steel had with my process to an enlargement of the grain of the metal as a result of the particular treatment employed. Microscopic examination indicates that as a result of the critical cold-reduction and following annealing and quenching operations the grain size is increased up to about five times that normally present. This grain size may be controlled to suit various applications by proper proportioning of initial cold-work and following annealing treatments. While the reasons for this grain enlargement are not entirely clear, it is my opinion that the critical cold reduction employed results in just sufllcient breaking up of the grains formed during the preceding annealing treatment to permit a free exercise of the surface energy of the grains. The small grains are taken up by the larger ones.

Thus it will be seen that there is provided in my invention a method of treating stainless irons and steels to give bars, rods and wire, as well as plate, sheetand strip and similar products, of

improved cold-forming properties, wherein the objects hereinbefore noted, together-with many thoroughly practical advantages are successfully achieved.

As many possible embodiments may be made 01' my invention, and as many changes may be made in the embodiment hereinbefore set forth, it will be understood that all matter described herein is to be interpreted as being illustrative and not as being a limitation.

I claim:

In manufactures of the class described, territic and martensitic stainless iron and steel bars, rods and wire of enlarged grain size and good cold-heading and cold-upsetting properties, said steel bars, rods and wire comprising 10% to 35% chromium and subjected to a cold-drawn reduction of 3 per cent to 15 per cent and a subsequent annealing treatment at a temperature of 1400 F. to 1800 l".

HENRY S. SCI-IAUF'US. 

